Role of thermal conditions in habitat selection by hydrothermal vent gastropods

Habitat selection by 3 Juan de Fuca Ridge gastropod species relates to their thermal environment. Both collections and images taken along transects document the small-scale abundance patterns of each species with respect to temperature and distance from vent flows. Lepetodrilus fucensis and Depressigyra globulus were most abundant at distances from vent flows of 0 to 25 cm in warm fluids with high temperature variability (10 +/- 5 degrees C) over several time scales. Both species were also abundant at 26 to 50 cm, where temperatures were lower with less variability (4 +/- 1 degrees C). Provanna variabilis was most abundant from 51 to 75 cm, where temperatures were stable (3 +/- 0.5 degrees C). All species were absent where maximum fluid temperatures reached 18 degrees C and their substratum coverage was related to temperature. When presented with a choice in vent fluids from 10 to 2 degrees C, L. fucensis and D. globulus moved to areas with temperatures above 5 degrees C, while P. variabilis showed no preference. In species-specific temperature preference experiments, L. fucensis and. D. globulus aggregated between 5 and 1.3 degrees C, while P. variabilis occupied areas with significantly lower temperatures from 4 to 11 degrees C. These experimental temperature preferences correspond with their thermal environments. Upper temperature limits are moderate; extreme abiotic variability in higher temperature fluids may constrain these 3 species. We conclude thermal conditions are a primary determinant of habitat selection, thereby driving gastropod abundance patterns. However, other factors likely contribute. Space competition nearest vent flows may result in the displacement of individuals of these species to low quality habitats.